The present invention generally relates to metal-oxide-semiconductor field-effect transistors (MOSFET), and more specifically, to source/drain contact structures.
The MOSFET is a transistor used for amplifying or switching electronic signals. The MOSFET has a source, a drain, and a metal oxide gate electrode. The metal gate is electrically insulated from the main semiconductor n-channel or p-channel by a thin layer of insulating material, for example, silicon dioxide or glass, which makes the input resistance of the MOSFET relatively high. The gate voltage controls whether the path from drain to source is an open circuit (“off”) or a resistive path (“on”).
N-type field effect transistors (NFET) and p-type field effect transistors (PFET) are complementary MOSFETs. The NFET uses electrons as the majority current carriers and is built directly on a p-type substrate with n-doped source and drain junctions (also called epitaxial contacts) and an n-doped gate. The PFET uses holes as the majority current carriers and is built on an n-well with p-doped source and drain junctions (epitaxial contacts) and a p-doped gate. The dopant concentration in the source and drain junctions is an important parameter for optimal transistor function.